The following commands has been tested and used on ffmpeg-20160114-git-62dfe1d-win64-shared.7z on Windows 10 Pro

Presets can be ultrafast, superfast, veryfast, faster, fast, medium (default), slow and veryslow

Only use ultrafast if your media is not important, and you need the fastest speed.
My friend butcha says you shouldn't go lower than veryfast. Which sounds like a good idea if your video is important.

The lower the better and bigger file size.

I have tested and recommend the following:

• 19-20 for PAL

Suggestion: Compare it yourself!!

ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=10 -t 25 output10.mkv
ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=15 -t 25 output15.mkv
ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=18 -t 25 output18.mkv
ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=19 -t 25 output19.mkv
ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=20 -t 25 output20.mkv
ffmpeg -i title00.mkv -c:v libx265 -preset ultrafast -x265-params crf=23 -t 25 output23.mkv

I used MakeMKV on windows, to make sure I only got what I needed. MakeMKV depends on the speed over your harddrive, as there's nothing being transcoded.

After getting the title00.mkv(860MB) from MakeMKV, you can feed it to ffmpeg, to generate a small output.mkv (212MB) using:

ffmpeg -i title00.mkv -map 0 -c copy -c:v libx265 -preset ultrafast -x265-params crf=20 output.mkv

This should keep original sound & subtitle tracks :)

Using a MakeMKV, it takes 18s to convert a whole 4.76GB ISO to 4.69GB title00.mkv. FFMPEG transcoding with the above command, takes 460.88s (9.77x speed) on my i7-4770k and generated a 712MB output.mkv

Using those numbers, that means I should be able to convert and transcode 187 ISO's daily on my desktop. Unfortunately I don't have such a large collection, but it's definately a good thing to do if you have a lot of ISO's and want to save some space :)

Put this script in the same location as where the bin folder is. Or just change the script to your needs..

Usage: Drag & drop the files onto your .bat file.
Setup: Read the script, understand it.. remove the rem word if everything looks good.

@echo off
echo.
echo Last chance to chicken out...
timeout 10
set "scriptDir=%~dp0"
set "append_to_filename= x265"
if [%1]==[] goto :eof
set n=0
:loop
echo.
echo Script dir: "%scriptDir%"
echo Input: "%~f1"
echo Output: "%~dp1%~n1%append_to_filename%.mp4"
cd %scriptDir%/bin/
rem ffmpeg -i "%~f1" -c:v libx265 -preset veryfast -x265-params crf=19 -c:a aac -strict experimental -b:a 128k "%~dp1%~n1%append_to_filename%.mp4"
shift
set /a n+=1
if not [%1]==[] goto loop
pause